The present invention relates to a gas scrubber used in fabricating semiconductor devices for scrubbing used gases and a gas filtering method using the same.
In general, chemical gases are used in various processes such as thermal treatment, thin-film formation and etching for fabricating semiconductor devices. The gases used in these processes are scrubbed through several steps and then recycled.
FIG. 1 is a schematic diagram showing a typical gas scrubber for a semiconductor device, and particularly, a gas scrubber for scrubbing silane (SiH.sub.4) gas. In FIG. 1, reference numeral 1 denotes a used gas inlet, reference numeral 3 denotes an air inlet, reference numerals 5, 7 and 9 denote first, second and third gas lines, reference numeral 14 denotes a filtering portion, reference numeral 16 denotes a catalytic reaction chamber, reference numeral 18 denotes a blower, and reference numeral 20 denotes a check valve.
The used gas which is to be scrubbed, i.e., silane (SiH.sub.4), entering via the used gas inlet 1 produces a silicone dioxide powder and vapor by reacting with the air entering via the air inlet 3: SiH.sub.4 +20.sub.2 .fwdarw.SiO.sub.2 +2H.sub.2 O. The SiO.sub.2 powder is removed by the filtering portion 14. Then, the unreacted used gas flows into the catalytic reaction chamber 16 through the first gas line 5 and is then reprocessed by a catalytic solution. Thereafter, the gas scrubbed by the filtering portion 14 or catalytic reaction chamber 16 passes through the second gas line 7, for output through third gas line 9. The blower 18 is installed to prevent pressure loss caused when the filtering portion 14 become blocked by the powder.
In the gas scrubber, the durability of the gas scrubber is directly related to that of the filtering portion 14. Accordingly, increasing the life span of the filtering portion 14 will reduce the cost of a gas scrubber used in fabricating semiconductor devices.
FIG. 2 is an exploded perspective view of the filtering portion of the conventional gas scrubber. Here, reference numeral 20 denotes a flange, reference numeral 22 denotes a first gas inlet, reference numeral 24 denotes a second gas inlet, reference numeral 30 denotes a sealing ring, reference numeral 32 denotes a clamp, reference numeral 40 denotes a filter having an inlet A, and reference numeral 50 denotes a hollow housing.
The filtering portion of the conventional gas scrubber is comprised of the flange 20 having first and second gas inlets 22 and 24 installed on the upper and lower surfaces thereof, respectively, the hollow housing 50 combined at one end with the outer circumferential surface of the flange 20, and a filter 40 housed in the hollow housing 50 and fixed to the second gas inlet 24 by the clamp 32.
Here, the hollow housing 50 is used for protecting the filter 40 from being damaged by an external impact. The sealing ring 30 is inserted between the flange 20 and the hollow housing 50 to fix the former to the latter, thereby buffering impacts generated at the contact surface between the flange 20 and the hollow housing 50 and preventing the leakage of the gas introduced into the filter 40.
The powder and vapor which are generated by the reaction of the used gas with air, and the remaining non-reacted used gas pass through the flange 20 via the first gas inlet 22, flow into the filter 40 through the second gas inlet 24, and then flow out of the filter 40 as indicated by the arrows of FIG. 2. At this time, the vapor, and the remaining non-reacted used gas penetrate through the filter 40, but the powder is collected at the inner walls of the filter 40. Accordingly, in the conventional gas scrubber, the life span of the filtering portion is shortened due to the following problems.
First, since the filter 40 must be fixed to the second gas inlet 24, it is inherent that the filter inlet A is the narrowest portion of the filter itself. Accordingly, during filtering, the filter inlet becomes partially blocked with powder which accumulates on the inner walls of the filter. This phenomenon is the main cause of the life reduction of a filter since the accumulation of powder at the filter inlet requires exchange of a whole filter despite the fact that the other portions thereof are free of powder build up.
Second, in the conventional device, the filtered powder collects on the filter's inner wall, which has an adverse effect on the life of a filter. That is, if the filtered powders were collected on the outer wall of the filter 40, the accumulation of powder could be eliminated, simply by periodically jarring the exterior wall. Here, it should be appreciated that interior powder accumulation is difficult to remove and results in early filter replacement.
Third, the shape of the filter 40 becomes distorted when it is loaded into the hollow housing 50, such that the effective surface area for filtering is reduced. Since the durability of a filter is directly proportional to the surface area where powder may accumulate, if this area is increased, the life of the filtering portion is prolonged.